1. Field of the Invention
The present invention relates to a method for fabricating a metal plug for electrically connecting metal wiring layers, respectively over and beneath an interlayer insulating film in a highly integrated semiconductor device, and more particularly to a method for forming a contact hole in such a semiconductor device, capable of improving an integration degree.
2. Description of the Prior Art
Generally, highly integrated semiconductor devices such as direct random access memories (DRAMs), static random access memories (SRAMs) and application specific integrated circuits (ASICs) have a structure including a plurality of wiring layers, a plurality of interlayer insulating films, each interposed between vertically adjacent wiring layers, and a contact formed in each interlayer insulating film and adapted to electrically connect the wiring layers associated with the interlayer insulating film. As the dimension of the contact is larger, the highly integrated semiconductor device has a higher integration degree. The dimension of the contact is determined by the dimension of the contact hole. However, it is impossible to reduce the dimension of the contact hole below a certain level due to limitation on semiconductor fabrication equipment such as light exposure devices. As a result, the conventional highly integrated semiconductor devices have a limitation on the integration degree.